| Summary: | The Early Jurassic Nordegg Member in north-eastern British Columbia (NEBC) is
composed of 25-30 m of organic-rich marine strata. The unit was deposited in a
restricted basinal environment, west of a high standing carbonate platform.
The Nordegg Member consists of four lithological facies: (A) a basal
conglomeratic lag deposit; (B) a lower phosphatic marlstone that was deposited during
highly productive conditions; (C) an overlying marlstone which represents an anoxic
phase of sedimentation; and (D) an upper phosphatic mudstone reflecting a productive
water column. Geochemical analysis reveals depositional conditions where high
productivity is associated with enrichments of P and Fe, K, Ti, V, Cr and Zn and total
organic carbon values (TOC) between 0-8 wt%, likely due to upwelling currents
introduced nutrient-rich water increasing algal productivity during relative sea-level rise.
The marlstone contains higher TOC (6-20 wt'%) and reduced concentrations of P, Fe, K,
Ti V, Cr and Zn. The elevated TOC's and lack of productivity-proxying elements (e.g.
P) infers organic matter incorporation into the sediment was primarily controlled by
redox conditions when basin conditions were persistently anoxic.
The TOC concentrations are a reflection of the depositional environment and have
a strong influence on potential gas capacity. The TOC-rich samples have improved
adsorption capacities compared to their organic-lean counterparts due to the highly
microporous nature of organic matter to which the gas molecules physically adsorb to.
Nordegg adsorbed gas capacities range from 0.05 cc/g to over 2 cc/g in organic-rich
zones.
The relationship between TOC and adsorption is complicated by other geologic
factors including moisture. Moisture competes for adsorption sites with methane and
blocks pores and pore-throats, reducing the transmissibility of the methane to the
microporosity of the organic matter.
Twenty to eighty percent of total gas storage is free gas (gas occupying open
pores), ranging from 0.1 - 1.3 cc/g. Nordegg total gas-in-place ranges from 1 - 24
BCF/section. The greatest potential for gas shale production is to the south-west of the
study area (93-P-5). TOC concentrations (up to 20 wt%), thickness, maturity and
fracture-potential improve the gas shale potential in this region making it a prime gas
exploration target. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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